2152 A TEXTBOOK OF THEORETICAL BOTANY 



The most authoritative classification of the Ferns based on Hving forms 

 is that of Christensen in his " Index Fihcum", which is summarized in the 

 " Manual of Pteridology " (1938). 



I. Filicales Eusporangiatae 



1. Ophioglossales 

 {a) Ophioglossaceae 



2. Marattiales 



(a) Angiopteridaceae 



(b) Marattiaceae 

 II. Filicales Leptosporangiatae 



I. Filicales 



(a) Osmundaceae 



(b) Schizaeaceae 

 (f) Marsileaceae 

 (d) Gleicheniaceae 



THE SPERMATOPHYTA 



The older classifications did not recognize the Spermatophyta as a 

 distinct phylum, but separated plants into Cryptogamia and Phanerogamia. 

 The former embraced all the groups we have so far mentioned in this 

 chapter while the latter included the Gymnospermae and the Angiospermae. 

 The discovery of the Pteridospermae, as we have seen, opened up a new 

 viewpoint, for it indicated that the separation of the Phanerogamia was not 

 so fundamental as had been previously thought. We find, therefore, that 

 these terms, Cryptogamia and Phanerogamia, became less and less used in 

 modern classification, while the phylum Spermatophyta replaced the latter 

 term and is used to include the three main groups: 



1. Pteridospermae 



2. Gymnospermae 



3. Angiospermae 



The more detailed classification of these three sub-phyla can be best 

 treated separately. 



THE PTERIDOSPERMAE 



The classification of all fossil plants presents special difiiculties and the 

 Pteridospermae are in some ways the most difficult group, inasmuch as the 

 limits of the group are still unknown. Fossil plants are often discovered 

 piecemeal and each portion is named and described separately. Only in 

 relatively few cases is enough of the plant known to give us a reasonably 

 clear idea of its general structure. Differences in the mode of preservation 

 add to the obscurity, some parts of plants being known both anatomically 

 and externally, while the majority are only known under one aspect 



